The present invention relates to a hydrostat for a portable gas range, and more particularly, to a hydrostat for automatically discharging gas, which is overcompressed into a gas container installed in a portable gas range when the inner pressure of the gas container continuously increases due to a radiant heat even after gas flow is usually blocked by a container-detaching safety device extinguishing a fire when an abnormal pressure occurs within the gas container, thereby preventing the gas container from exploding.
Generally, gas ranges are widely used when preparing a light meal or dish outdoors or indoors. Due to portability and convenience, the number of gas range users and the possible uses of gas ranges have increased. Accordingly, various safety devices have been developed to reduce accidents associated with gas ranges.
As shown in FIGS. 1 through 3, a general portable gas range 1 includes a container guide 5 which guides a gas container 3 in association with the down motion of an installing/detaching lever 2 so that the gas container 3 is installed to a governor valve 4 in a horizontal direction. The portable gas range 1 also includes a spark plug 6, a control lever 7 for controlling the strength of spark and combustion, a burner 8 for providing flames, and a cover 9 for covering the gas container 3. As shown in FIG. 2, when the installing/detaching lever 2 is pulled down, the container guide 5 moves forward so that the gas container 3 is installed to the governor valve 4. When the installing/detaching lever 2 is pushed up, the container guide 5 moves backward so that the gas container 3 is detached from the governor valve 4.
When the inner pressure of the gas container 3 reaches a dangerous level, the installing/detaching lever 2 moves up due to the operation of a container-detaching safety device, so the container guide 5 moves backward detaching the gas container 3 from the governor valve 4, thereby preventing the overpressure of the gas container 3. As shown in FIG. 3, in a state in which the gas container 3 is detached from the governor valve 4, when the inner pressure of the gas container 3 reaches a deforming pressure due to a radiant heat, a deformable portion 3a, which is provided at the top of the gas container 3, swells so that the outlet of the gas container 3 closely contacts the governor valve 4. In the case of a flow-blocking type portable gas range, when the inner pressure of a gas container reaches a dangerous level, the flow path of a governor valve is blocked by the operation of a flow-blocking safety device to prevent overpressurization of the gas container.
However, the present invention provides a hydrostat for the portable gas range 1 to prevent the gas container 3 from exploding by automatically discharging overcompressed gas from the gas container 3, when the inner pressure of the gas container 3 continuously increases to a threshold value of deformation, even after gas flow is primarily blocked by an existing safety device and a fire may have been extinguished.
Generally, when gas is supplied from a gas container to a portable gas range, the temperature of the gas container decreases due to the latent heat of vaporization, which is generated by gas absorbing surrounding heat while vaporizing, such that the probability of a gas explosion due to an increase in temperature is low.
However, since a cooker mounted on a portable gas range is heated, a radiant heat from the bottom of the cooker may be transmitted to a gas container. Here, when the radiant heat is more than the latent heat of vaporization, which is taken away from the gas container while the gas of the gas container vaporizes, heat corresponding to a difference between the radiant heat and the latent heat of vaporization is accumulated at the gas container, thus increasing the temperature of the gas container. Expansion of gas due to the increase of the temperature results in an increase in the inner pressure of the gas container.
In the Republic of Korea, only portable gas ranges, in which gas flow is automatically blocked for extinguishing a fire when the inner pressure of a gas container is in a range of 5–7 kg/cm2, are permitted to be manufactured and sold. In Japan, only portable gas ranges, in which gas flow is automatically blocked for extinuishing a fire when the inner pressure of a gas container is in a range of 4–6 kg/cm2, are permitted to be manufactured and sold.
To block the gas flow, there is provided a safety device. In the Republic of Korea, a container-detaching safety device blocks the gas flow by detaching a gas container from the inlet of a governor of a portable gas range when the inner pressure of the gas container is in a range of 5–7 kg/cm2. In Japan, a flow-blocking safety device blocks the gas flow by blocking a flow path within a governor of a portable gas range when the inner pressure of a gas container is in a range of 4–6 kg/cm2. The container-detaching type is mainly used in the Republic of Korea, and the flow-blocking type is mainly used in Japan.
These safety devices are provided for preventing the explosion of a gas container due to an increase in the inner pressure of the gas container, which results from the expansion of gas that occurs when the temperature of the gas container is increased by accumulation of heat corresponding to the difference between a radiant heat and the latent heat of vaporization where the radiant heat is more than the latent heat of vaporization.
For example, it is defined that the normal pressure of a butane gas container used in a portable gas range is in a range of 2–3 kg/cm2, the primary deforming pressure of the gas container is 13 kg/cm2, and the secondary deforming pressure of the gas container is 15 kg/cm2. In other words, it is regulated that the gas container be manufactured to not explode until the inner pressure of the gas container reaches 15 kg/cm2. Accordingly, an explosion of the gas container can be prevented by blocking the flow of gas at the inner pressure of 5–7 kg/cm2 and extinguishing a fire when the inner pressure of the gas container increases due to a radiant heat in order to prohibit the inner pressure of the gas container from increasing to the threshold value of explosion.
As shown in FIGS. 4 and 5, a body 11 of a flow-blocking safety device includes an inlet 11a which a gas container 3 is installed to or detached from; a chamber 12 for maintaining the gas pressure, which is supplied to a burner, constant; a control lever 14 for controlling the volume of gas supplied to the burner; and a flow path for connecting the inlet 11a, the chamber 12, and the control lever 14.
A gas blocking unit 50 for blocking the flow path when a gas pressure exceeds a reference value is provided in the flow path between the inlet 11a and the chamber 12. A pressure control unit 30 for maintaining the pressure of gas, which is supplied to a burner, constant is installed within the chamber 12. The gas blocking unit 50 is composed of a taper hole 51 whose diameter decreases toward the back of the flow path, a cylinder hole 52 which straightly communicates with the taper hole 51, a blocking valve 53 which is installed within the taper hole 51 and the cylinder hole 52 and is moved backward by the pressure of gas, and a plate spring 54 which elastically supports the back of the blocking valve 53. The plate spring 54 contacts a return valve 55 whose one end is exposed to the outside. A return lever 56, which slides up and down and pushes forward the return valve 55, is installed outside above the return valve 55.
The blocking valve 53 is composed of a blocking portion 57, which is located in front of the taper hole 51, and an operating portion 58, which is located within the cylinder hole 52. An O-ring is installed around the outer circumference of the blocking portion 57 in order to hermetically seal the taper hole 51 when the blocking valve 53 moves backward, and an O-ring is installed around the outer circumference of the operating portion 58 in order to prevent the leakage of gas.
In addition, a nozzle 59 communicating with the chamber 12 is provided at one side of the cylinder hole 52 in front of the operating portion 58.
The pressure control unit 30 includes a rubber plate 31 which is hermetically sealed in an upper portion of the chamber 12; a spring 32 which presses down the rubber plate 31; a needle holder 33 which is connected to the rubber plate 31; and a needle valve 35, which is connected to the body 11 via a hinge at the center, is connected to the needle holder 33 at one end, and has a stopper 34 for closing and opening the nozzle 59 at the other end.
Accordingly, when a user turns on the gas range, gas within the chamber 12 is supplied to the burner, decreasing the gas pressure within the chamber 12, so the rubber plate 31 is pressed by the spring 32 separating the needle valve 35, which is hinge-connected to the body 11, from the nozzle 59 so that gas in a gas container flows into the chamber 12.
When the pressure of gas flowing into the chamber 12 exceeds a predetermined value, the rubber plate 31 overcomes the elasticity of the spring 32 and is lifted up so that the needle valve 35 blocks the nozzle 59.
In addition, when the gas pressure exceeds a reference value due to the overheating of the gas container, the blocking valve 53 overcomes the elasticity of the plate spring 54 and moves backward blocking the taper hole 51 so that gas supply is interrupted and the fire of the burner is extinguished.
The above-described flow-blocking safety device cannot cope with a rapid increase of pressure within the gas container, which still remains within the gas range after the gas supply is interrupted primarily, due to a radiant heat occurring after the heat of vaporization, which is generated when liquefied gas within the gas container vaporizes.
In many cases, the explosion of a gas container has been prevented by interrupting the gas supply at a dangerous pressure level. However, there have been constant accidents where a gas container explodes even after a safety device operates.
Recently, an approach for preventing the explosion of a gas container was disclosed in Korean Patent Application No. 2000-0065187.
FIG. 6 is a side-sectional view of a safety device for a portable gas range, as disclosed in Korean Patent Application No. 2000-0065187. The safety device further includes a gas discharge unit 60 in addition to a flow-blocking safety device for a portable gas range. The gas discharge unit 60 is composed of a housing 61 which includes a through-hole 61a communicating with a flow path and a discharge hole 61b for discharging gas outside; and a safety bar 63 which is elastically supported by a spring 62 so that it closely contacts the through-hole 61a. 
A cylinder hole 64 is provided within the housing 61. The through-hole 61a is provided at one end of the cylinder hole 64, and a circular cap 65 is screw-connected to the other end of the cylinder hole 64. The discharge hole 61b is provided at the circumferential wall of the cylinder hole 64 near the through-hole 61a, and a nozzle 66 extending outside is connected to the discharge hole 61b. 
The safety bar 63 is composed of a piston portion 63a, which is inserted into the cylinder hole 64 within the housing 61 so that it is moved by a gas pressure; and a sealing portion 63b, which closely contacts the through-hole 61a. The spring 62 supported by the inner wall of the cap 65 is provided at the back of the safety bar 63.
Accordingly, as described above, when the pressure of gas within the chamber 12 exceeds a predetermined value, the needle valve 35 of the pressure control unit 30 blocks the nozzle 59, primarily interrupting the gas supplied to the chamber 12. Continuously, the gas container is overheated increasing the pressure of supplied gas over the reference value. Then, the plate spring 54 operates to secondarily interrupt the gas supply so that the fire of the burner is extinguished.
In this state, when the gas pressure of the gas container exceeds a predetermined value, for example, 13–15 kg/cm2, due to a fire occurring near the gas range or a latent heat which is accumulated in the gas range or the gas container, the safety bar 63 of the gas discharge unit 60 overcomes the elasticity of the spring 62 and moves backward opening the through-hole 61a. As a result, gas within the gas container is discharged outside through the nozzle 66, decreasing the inner pressure of the gas container. Accordingly, even if the gas container is continuously overheated, it can be safely used without exploding.
However, in this conventional embodiment, since the housing 61 is formed to have the through-hole 61a extending from the taper hole 51, the structure is complicated. In addition, since the gas discharge unit 60 protrudes from the side of the body 11, the volume of the body 11 increases, which requires a structural change in a usual portable gas range.
Since the through-hole 61a of the housing 61 is not simply a gas passage but is mechanically connected to a primary safety device, which is operated by the plate spring 54, it is necessary to separately manufacture the housing 61 from the body 11 in order to operate the blocking portion 57 using the spring 58a. Accordingly, a process of assembling the body 11 and the housing 61 is additionally needed.
Moreover, the discharge hole 61b needs to be formed within the gas range so that gas is discharged preferably downward or outside using a connection pipe. For this, the extra nozzle 66 must be formed, so the entire structure of the safety device becomes complicated.
In the case of the container-detaching safety device for detaching a gas container from a gas range, since an external mechanical unit needs to be installed, the ratio of defective products to finished products is high. When it is used for a long term, an operating portion easily corrodes or is easily contaminated with foreign substances, so the safety device does may not operate even if the inner pressure of the gas container increases to a dangerous value.
Moreover, the container-detaching safety device, which detaches the gas container using the external unit, requires a great power to forcibly detach the gas container and also increases in size.
Although the latent heat of vaporization disappears shortly after a container-detaching safety device or a flow-blocking safety device blocks the path of gas flow so as to extinguish a fire when the pressure of a gas container increases over a predetermined value, the gas container totally absorbs a radiant heat from a cooker, such as a frying pan, even after the fire is extinguished, so the pressure of the gas container rapidly increases. As a result, the inner pressure of the gas container exceeds a primary container deformation pressure and reaches a secondary container explosion pressure, exploding the gas container.
The use of larger cookers may further increase the chances for container explosion. According to “(5-1) The use of a larger cooker than a tripod” at “Paragraph 5—The Incidents Related to Portable Butane Burners (Portable Gas Ranges) and Combined Containers (Butane Gas Containers)” of the Gas Incident Yearbook (Chapter 4, pp. 185, 2000) published by Korea Gas Safety Corporation, the cause of some incidents occurs since a larger cooker than the tripod of a portable butane burner was used. The combined container installed in the burner was heated by a radiant heat and exploded due to an increase in the inner pressure thereof. For example, while meat was being roasted using a portable butane burner, an overpressure cutoff of the burner operated, and after a short time, a butane can exploded with a bang sound.
This report indicates that a gas container exploded even when an existing safety device operated normally. In other words, the fact that the gas container exploded with a bang sound after the existing safety device operated suggests that while the latent heat of vaporization disappears after gas flow is blocked, a radiant heat is still applied to the gas container rapidly increasing the inner pressure of the gas container over a deforming pressure to an explosion pressure, so the gas container explodes. Consequently, it further suggests that existing safety devices cannot fundamentally prevent explosion of a gas container.
Accordingly, development of a new safety device for fundamentally preventing the explosion of a gas container in a portable gas range is desired.